Dellorto carb trouble shooting

[yellerduck]

I have a 1990 750 Sport that has two Dellorto PHF 36 carbs. I am having a problem with one of them leaking. I ordered an original seal kit and replaced all the seals I could find.

When I turn the key, the fuel pump starts and after a few seconds, fuel starts pouring out of the little overflow valve. The floats don't seem to be sticking, I cleaned everything up really well with carb cleaner.

I have a fuel pump and have read where a lot it is said I should remove it. However, the bike has been running for years with it and the Dellorto carbs with the previous owner and I don't know if I should or should not remove it.

Someone else told me that the float needle valve could be bad. If so, how the heck do you remove the pin that holds the floats in as I am assuming you would have to remove it to replace the float needle valve.

Any suggestions?

[DesmoDog]

It's been a while since I rebuilt mine, but I seem to remember that one end of that pin sticks out so you can grab it with a Vise Grip and pull it out.

[yellerduck]

Yeah, that worked (wire cutters to pull it out) . Mine was in tight!

[ducinthebay]

The Dellortos can't take the full pressure of the fuel pump. You will need to run a return line in your fuel system. The tank has the main petcock in the back of the tank, a vent line, and a fuel return line next to eachother near the middle of the tank. You need to put a T in the fuel line down by the carbs and run that back up into the tank. In my system I used two T's, right in line with eachother, one for the return, and the other to split the line to the two carbs and ran that whole thing between the carbs, almost on the cases. I also installed the plastic quick release connectors which make the job of jetting much easier.

The Sport can not run for very long without the fuel pump as the pickup hose in the tank is brazed in, and ends half way up the tank. Without a fuel pump you will have only about 1.5 gallons of usable gas before you start sucking air.

Hope this helps.

Phil
90 Sport

[yellerduck]

Hey Phil, mine already had two t's in the fuel line just as you describe. I fixed the problem by ordering a new float needle valve and adjusting the float down a bit. Now when I turn the pump on I can hear the girgling of the fuel being returned into the tank. I can honestly say that is a beautify sound! Thanks to all for the advice.